Maximum aperture

The biggest aperture a lens offers, with the smallest f-number, which admits the most light.

In a prime lens and some zoom lenses the maximum aperture is constant.

In some zoom lens the maximum aperture changes as the focal length is altered. If so it is quoted as a range: for example, an 18-55 f/3.5-5.6 lens will have a maximum aperture of f/3.5 at 18mm focal length, and a maximum aperture of f/5.6 at 55mm focal length.

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